3-Panel transmissive projection system

ABSTRACT

The invention relates to a 3-panel transmissive projection system. In particular, the invention relates to a 3-panel transmissive projection system applying reflective type polarizers for both polarizing and analyzing operations in the projection system.

FIELD OF THE INVENTION

The invention relates to a 3-panel transmissive projection system. Inparticular, the invention relates to a 3-panel transmissive projectionsystem applying reflective type polarizers for both polarizing andanalyzing operations in the projection system.

BACKGROUND OF THE INVENTION

Projection systems, such as described in, for example, US patentapplication no. 2002/0015135, generally use a reflective LCD array witha single polarizing beam splitter. However, by combining the light pathfrom the light source and the display panels with the light path betweenthe display panels and the projection lens, the light paths cannot beoptimized individually.

The high-temperature (HT) polyfilm technology provides high brightnessusing small miniaturized LCD panels. However, the combination ofminiaturisation and high light output causes extreme high lightdensities in the light path, thus limiting the lifetime expectancy ofthe LCD panels and polarizing films. The manufacturers of HT polyfilmprojection systems continuously improve the lifetime expectancy of theLCD panels. However, improvements in the lifetime expectancy of thepolarizing films has almost come to a halt. Hence, the lifetimeexpectancy of the HT polyfilm projection system is limited by thelifetime of the polarizing films.

OBJECT AND SUMMARY OF THE INVENTION

It is an object of the present invention to provide a projection systemhaving high brightness capabilities in combination with an improvedlifetime expectancy.

It is a further object of the present invention to provide atransmissive type projection system, such as transmissive HT Polysilicon LCDSs, so as to ensure that the light path between the lightsource and the display panel(s) and the light path between the displaypanel(s) and the projection lens are completely separated, and thereforemay be optimized individually, leading to a higher system efficiency andto a higher brightness.

A particular advantage of the present invention is the provision of alow-cost projection system having a high brightness and a long lifetimeexpectancy by using miniaturized transmissive display panels.

A particular feature of the present invention relates to the provisionof polarizers for the analyzing operation and for the polarizationoperation of the projection system.

According to a first aspect of the present invention, this object isachieved by a projection system for projecting an image onto aprojection surface, the projection system comprising:

-   -   (a) a light source for supplying light;    -   (b) an optical element for gathering and focusing said light,        thereby providing a light beam;    -   (c) a first reflective polarizer for polarizing said light beam,        thereby generating a polarized light beam;    -   characterized in that the projection system further comprises:    -   (d) a transmissive display panel for receiving said polarized        light beam and for manipulating said polarized light beam,        thereby encoding image information on said polarized light beam        and generating an encoded light beam;    -   (e) means for controlling each pixel of said transmissive        display panel so as to control manipulation of said polarized        light beam; and    -   (f) a second reflective polarizer for rejecting unwanted        polarizations of said encoded light beam and for transmitting        desired polarization of said encoded light beam to said        projection surface.

In this context, the term image is to be construed as a frame of a videosequence, a still photograph or a still digital representation or anycombination thereof

The second reflective polarizer according to the first aspect of thepresent invention may be oriented with respect to the encoded light beamat incident angles in the range between approximately 30° and 60°, suchas incident angles of 35°, 45° or 55°. By orienting the secondreflective polarizer acting as an analyzer at an angle of approximately45°, ghost images generated by light bounced back from the secondreflective polarizer to the display panel are avoided.

The projection system according to the present invention may be realisedby folding the light path from the light source to the projectionsurface in a two-layer structure. By folding the light path, theprojection system advantageously provides a very compact projectionsystem.

The transmissive display panel may comprise an electro-optical mediumsuch as liquid crystal or plasma, or electrochromic or electrophoreticelements, light-emitting elements, organic or inorganic light-emittingelements, polymer light-emitting elements, or any combination thereof.Any type of display element may be used for the transmissive displaypanel as long as the display substrates are transparent or opaque. Theflexibility of a transmissive display panel type provides a projectionsystem which may be designed in accordance with a wide variety ofcustomer requirements or specifications.

The means for controlling each pixel of the transmissive display panelaccording to the first aspect of the present invention may beimplemented by using any processor techniques known to persons skilledin the art. The means for controlling each pixel may be incorporated onthe transmissive display panel substrate, thereby reducing the requiredspace and optimizing the production costs.

The second reflective polarizer may comprise a Moxtek™ beam splitter. Byutilising a Moxtek™ beam splitter for the analyzing operation of theprojection system, an excellent brightness, low cost, and long lifetimeexpectancy are obtained. The Moxtek™ beam splitter removes thedisadvantages of the polarizer films.

BRIEF DESCRIPTION OF THE DRAWINGS

The above, as well as additional objects, features and advantages of thepresent invention, will be better understood from the followingillustrative and non-limiting detailed description of preferredembodiments of the present invention, with reference to the appendeddrawings, wherein:

FIG. 1 is a schematic diagram of the elements and light path for onecolour in the preferred embodiment of the present invention; and

FIG. 2 is a detailed diagram of the elements and light paths for red,green and blue colours, shown unfolded for the sake of simplicity, ofthe preferred embodiment of the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

In the following description of various embodiments, reference is madeto the accompanying Figures which form a part thereof, and in whichvarious embodiments in which the invention may be practised are shown byway of illustration. It is to be understood that other embodiments maybe utilized, and structural and functional modifications may be madewithout departing from the scope of the present invention.

FIG. 1 shows a projection system, designated in its entirety byreference numeral 10, for projecting images onto a projection surface12. The projection system 10 comprises a light source 14 supplying thelight to be transmitted through the projection system 10. The projectionsurface 12 may be formed on any type of surface such as a white wall ora projector screen.

The light source 14 supplies light to an optical element 16 forgathering and focusing the light, thereby providing a light beam. Theoptical element 16 may be implemented by a rod integrator. The opticalelement 16 comprises a first end 18 for receiving the light and a secondend 20 for providing the gathered and focused light. A small colourseparation prism 22 is placed adjacent to the second end 20. An entrancesurface 24 of the colour separation prism 22 is substantially equal tothe surface of the second end 20. The colour separation prism 22separates the light into red, blue and green coloured light,respectively, which is subsequently reflected onto separate exit planesof the colour separation prism 22. For reasons of simplicity, FIG. 1shows only one light path for one colour.

The coloured light 26 exiting the colour separation prism 22 is directedthrough a first lens 28 focusing the coloured light 26 onto a firstpolarizer 30 which is transmissive to unwanted polarizations of colouredlight and reflective to desired polarizations, i.e. reflecting apolarized light beam 32. In an alternative embodiment of the presentinvention, the first polarizer 30 may be reflective to unwantedpolarizations of coloured light and transmissive to desiredpolarizations. This, however, obviously requires a change of the designand the light path from the light source to the projection surface.

In addition, the first polarizer 30 may be reflective to both desiredand undesired polarizations of the coloured light. The desiredpolarizations of the coloured light are directed in one direction andthe undesired polarizations are directed in another direction.

The polarized light beam 32 is focused through a second and third lens34 communicating the polarized light beam to a transmissive displaypanel 36 which modulates the polarized light beam so as to encode imageinformation thereon. The transmissive display 36 panel is controlled bya processor controlling each pixel of the transmissive display panel 36.

The transmissive display panel 36 may be implemented in a number ofways. By way of example, a transmissive display panel having an opaquesubstrate may utilise an electro-optical medium such as liquid crystalor plasma, or electrochromic or electrophoretic elements, light-emittingelements, organic or inorganic light-emitting elements, polymerlight-emitting elements, or any combination thereof

In the preferred embodiment of the present invention, the transmissivedisplay panel 36 utilises a liquid crystal display array.

As described above, the colour separation prism 22 is placed adjacent tothe optical element 16 so as to form an extension on the optical element16. Hence, the colour separation prism may be made very small. This,however, necessitates the coloured light to be expanded incross-sectional area so as to match the transmissive display panel 36.The expansion of the coloured light is performed by the second lens 34.

FIG. 1 shows a single transmissive display panel 36 for simplicity only.It is to be understood that each coloured light separated by the colourseparation prism 22 is communicated to a specific transmissive displaypanel.

The transmissive display panel generates an encoded light beam 38, whichis communicated to a second polarizer 40 operating as an analyzerrejecting unwanted polarizations of the encoded light beam from thelight path.

The second polarizer 40 is transmissive to unwanted polarizations of theencoded light beam and reflective to desired polarizations of theencoded light beam. In an alternative embodiment of the presentinvention, the second polarizer may be reflective to unwantedpolarizations of coloured light and transmissive to desiredpolarizations. This, however, obviously requires a change of the designand the light path from the light source to the projection surface.

As described with reference to the first polarizer 30, the secondpolarizer 40 may be reflective to both desired and undesiredpolarizations of the encoded light beam. The desired polarizations ofthe encoded light beam are directed in one direction and the undesiredpolarizations are directed in another direction.

In the preferred embodiment of the present invention, the first andsecond polarizers 30, 40 may be implemented by a Moxtek™ beam splitter.However, the first and second reflective polarizers 30, 40 may beimplemented by a wide variety of polarizers such as wire-gridpolarizers, cholesteric polarizers, interference films, holographicstructures, stacks of thin birefringent films, beam splitters, mirrors,or any combination thereof.

The polarized and encoded light 42 is received in a recombination prism44 gathering each polarized and encoded light beam from each colouredlight path, i.e. the red, green and blue light paths. The recombinedlight forms a complete image to be projected through a projection lens46 onto the projection surface 12.

The two prisms 22 and 44 may be implemented in a wide variety of ways.However, in the preferred embodiment of the present invention, theprisms 22 and 44 are implemented by a first and a second dichroic cube.

FIG. 2 shows a projection system designated in its entirety by referencenumeral 50. In contrast to FIG. 1, FIG. 2 shows three light paths: a redlight path 51 a, a green light path 51 b, and a blue light path 51 c.

Elements of the projection system 10 described with reference to FIG. 1,which are identical to elements in FIG. 2, are denoted by the samereference numerals.

The light source 14 supplies the light of the projection system 50, andthe optical element 16 focuses and gathers the light from the lightsource 14 prior to directing the light to a colour separation prism 22.The colour separation prism is shown in FIG. 2 as prisms denoted byreference numerals 22 a, 22 b and 22 c. The prism 22 a provides the redlight through the red light path 51 a to a first transmissive displaypanel 36 a. The prism 22 b provides the green light through the greenlight path 51 b to a second transmissive display panel 36 b. The prism22 c provides the blue light through the blue light path 51 a to a thirdtransmissive display panel 36 c.

Each transmissive display panel 36 a, 36 b and 36 c modulates the lightin accordance with the generation of particular images. The transmissivedisplay panels 36 a, 36 b and 36 c are controlled by one or moreprocessors controlling each pixel of the transmissive display panels 36a, 36 b and 36 c.

The encoded lights: encoded red, encoded green, and encoded blue areenhanced through sets of lenses 52 a, 52 b, 52 c and 54 a, 54 b and 54c. The sets of lenses allow the use of a very small dichroic cube forthe colour recombination prism 44.

As described with reference to FIG. 1, the light now recombined isprojected on the projection surface through a projection lens 46.

The projection system 50 may be folded into a two-layer configurationusing polarizers for the polarizing and analyzing operation, similarlyas described with reference to FIG. 1.

1. A projection system for projecting an image onto a projection surface(12), the projection system comprising: (a) a light source (14) forsupplying light; (b) an optical element (16) for gathering and focusingsaid light, thereby providing a light beam (26); (c) a first reflectivepolarizer (30) for polarizing said light beam (26), thereby generating apolarized light beam (32); characterized in that the projection systemfurther comprises: (d) a transmissive display panel (36) for receivingsaid polarized light beam (32) and for manipulating said polarized lightbeam (32), thereby encoding image information on said polarized lightbeam and generating an encoded light beam (38); (e) means forcontrolling each pixel of said transmissive display panel so as tocontrol manipulation of said polarized light beam (38); and (f) a secondreflective polarizer (40) for rejecting unwanted polarizations of saidencoded light beam (38) and for transmitting desired polarization ofsaid encoded light beam (38) to said projection surface (12).
 2. Aprojection system as claimed in claim 1, wherein said first and secondreflective polarizers comprise wire-grid polarizers, cholestericpolarizers, interference films, holographic structures, stacks of thinbirefringent films, beam splitters, mirrors, or any combination thereof.3. A projection system as claimed in claim 1, wherein said secondreflective polarizer (40) is oriented with respect to said encoded lightbeam at incident angles in the range between approximately 30°and 60°,such as incident angles of 35°, 45° or 55°.
 4. A projection system asclaimed in claim 1, wherein said projection system is realised byfolding the light path from said light source (14) to the projectionsurface (12) in a two-layer structure.
 5. A projection system as claimedin claim 1, wherein said transmissive display panel (36) comprises anelectro-optical medium such as liquid crystal or plasma, orelectrochromic or electrophoretic elements, light-emitting elements,organic or inorganic light-emitting elements, polymer light-emittingelements, or any combination thereof.
 6. A projection system as claimedin claim 1, wherein said means for controlling each pixel of saidtransmissive display panel (36) is implemented by using a processor. 7.A projection system as claimed in claim 1, wherein said means forcontrolling each pixel may be incorporated on said transmissive displaypanel substrate.
 8. A projection system as claimed in claim 1, furthercomprising an optical element (16) for gathering said light from saidlight source (14) and having an exit surface (20) adjacent to a colourseparation prism (22) having an entrance surface (24) which issubstantially equal to said exit surface (20).
 9. A projection system asclaimed in claim 8, wherein said colour separation prism (22) is adaptedto separate said light supplied by said light source (14) into red,green and blue coloured light.
 10. A projection system as claimed inclaim 1, wherein said transmissive display panel (36) comprises a first(36 a), second (36 b) and third (36 c) transmissive display panel unit,respectively.
 11. A projection system as claimed in claim 8, whereinsaid colour separation prism (22) is adapted to communicate red, greenand blue coloured light to said first (36 a), second (36 b) and third(36 c) transmissive display panel units.
 12. A projection system asclaimed in claim 1, further comprising a recombination prism (44) forrecombining encoded light beams into a single encoded light beam.
 13. Aprojection system as claimed in claim 12, wherein said recombinationprism (44) is adapted to receive encoded red, green and blue light fromsaid first (36 a), second (36 b) and third (36 c) transmissive displaypanel units, and said recombination prism (44) recombining said encodedred, green and blue light into a single encoded light beam to beprojected through a projection lens (46) onto said projection surface(12).
 14. A projection system as claimed in claim 11, further comprisingfocusing lenses (52 a, 52 b, 52 c and 54 a) for focusing said encodedlight before said colour recombination prism (44).
 15. A projectionsystem as claimed in claim 1, further comprising magnifying lenses (26,34) for providing a polarized light beam covering the full surface ofsaid transmissive display panel (36).